1. Field of the Invention
This invention relates to optical magnification systems. More specifically, this invention relates to monocular optical inspection systems.
While the present invention is described herein with reference to a particular embodiment for a particular application, it is understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional embodiments within the scope thereof.
2. Description of the Related Art
Visual inspection of manufactured products is a common practice in many fields of industry. For example, in the electronics industry inspection of components or soldering connections for defects which may render a device inoperative are routinely performed. Various means have been devised to aid the human eye in locating these and other types of defects by enlarging an image of the object under inspection through optical magnification.
One of the simpler optical magnification devices is commonly known as an eye loupe. An eye loupe may include one or more optical lens elements mounted in a housing generally cylindrical in shape. One using an eye loupe would typically hold one end of the loupe next to an eye and position an article to be examined at the opposite end of the eye loupe with a free hand. Alternatively, the object under inspection is often positioned on a planar observation surface and examined by a viewer translating the eye loupe just above the object. Both of the above modes of inspection have obvious shortcomings. In the former case both hands of the viewer are occupied, thus preventing simultaneous inspection and modification of the device under scrutiny. Viewers utilizing the latter mode of observation are subject to fatigue resulting from craning over the article under examination. Close proximity of the viewer to the examined object may result in contamination or may allow physical characteristics of the viewer such as a long nose or beard to partially obscure the object.
Microscopes provide another means of optical magnification which find application in a variety of industrial fields and overcome some of the disadvantages of eye loupes. In contrast to eye loupes microscopes are typically mechanically self supporting. This feature of self support allows simultaneous inspection and modification of an article under examination as the hands of a viewer are typically unconstrained while observing the article. Additionally, the face of a viewer is separated by a larger distance from an object under observation when a microscope rather than an eye loupe is used thereby reducing the chance of inadvertently contaminating or partially obscuring an object under view. Despite overcoming some of the disadvantages of eye loupes, microscopes often possess certain characteristics which may make them a less desirable means of optical magnification when utilized over extended periods. Specifically, commercially available microscopes typically have exit pupils on the order of 0.06 to 0.15 inch in diameter and eye relief of approximately 0.6 to 0.8 inch. An exit pupil is an area of space adjacent to the eyepiece of an optical instrument through which an observer may view an image of a magnified object. Eye relief refers to the distance from the eyepiece of an optical instrument to a point in space at which an observer is afforded a maximum field of view. Movement of a viewing pupil outside of the exit pupil or away from a plane parallel to the surface of the eyepiece at the eye relief distance may result in partial or total loss of view of the image of the object under magnification. The distance from this plane a viewer may move without experiencing significant loss of field of view generally increases with increasing eye relief. Hence, longer eye relief and enlarged exit pupils generally allow increased freedom of motion thereby reducing viewer fatigue.
The upright, linear structural configuration of many microscopes can also contribute to viewer fatigue. Specifically, this orientation often requires a craning of the neck to view an image through the microscope eyepiece. Moreover, this upright structure may prevent unaided line of sight viewing of the object under magnification unless the observer physically moves relative to the eyepiece. Convenient line of sight viewing may be important in applications involving modification of the object under magnification.
An optical magnification device better suited than many microscopes to applications requiring viewing periods of extended duration is the Metron 3-D Scanner manufactured by Metron Optics, Inc. of Solana Beach, Calif. The eye port of the device is located in a plane perpendicular to that of the object under magnification which allows a viewer to remain in an upright position. Additionally, an exit pupil of larger area than that of many microscopes enables a viewer greater freedom of motion thereby reducing fatigue. However, rather than being circular the exit pupil of the Metron is substantially trapezoidal in shape which imposes asymmetric constraints on viewer eye movement.
Included among other potentially undesirable characteristics of the Metron are its large size and substantial weight. Housing dimensions on the order of 22" limit the utility of the Metron in often cramped laboratories or in industrial applications already pressed for work station space. Further, the large optical elements within the Metron may be susceptible to extraneous light and reflections. Additionally, large optical elements are expensive to manufacture and the objective lens is not insulated from the working area containing the object under view. This lack of insulation increases the risk of contaminating optical elements of the device. Further, though larger than that of many microscopes the working distance between the objective lens of the Metron and the object being observed is less than desired for some applications.
Hence, a need in the art exists for a compact optical magnification system having substantial eye relief, a large and circular exit pupil, unaided line of sight viewing of an object under observation with minimal viewer movement, and a relatively large working distance between the object and an objective lens element of the magnification system.